The anatomy and function of cells in the olfactory system are well conserved through evolution. The similarities suggest that the physiological processes underlying odor detection depends on robust, yet obscure, biological principles. Diverse mechanisms underlie the transduction of odors into changes in cell excitability in olfactory receptor neurons (ORNs) in many species. The major aim of this proposal is to determine the types of odor-modulated ionic currents in a simple animal (the fruit fly, Drosophila melanogaster) that has reproducible behaviors to odors and is amenable to molecular and genetic analyses. The long-term goal is to understand the biological principles underlying how odor-induced changes in cellular excitability encode information about the identify of that odor. Whole cell and single channel (patch) recordings have been obtained for the first time (Figure 2) from cells in the main olfactory organ thereby allowing the genetic variability of Drosophila to be combined with state-of-the-art electrophysiological methods to study odor-modulated ion channel function and cellular excitability in wild type Canton-S flies. Two strategies will be used to identify odor-modulated conductances and intracellular second messenger pathways. Standard recording techniques will be used to determine the ionic basis of the odor-modulated currents. The involvement of various second messengers will be tested by their direct application to inside-out patches or to the cytosol via the patch pipet in whole cell recordings; pharmacological methods will be used to specifically block or activate particular enzymes. In complementary studies, the molecular nature of these modulated conductances and second messenger pathways will be investigated using mutant Drosophila strains with known defects in genes encoding ion channels and enzymes involved in signal transduction processes. Furthermore, the "enhancer trap" technique has been developed in Drosophila that allows mutation of genes expressed in subpopulations of cells. Using this technique, mutants defective in their olfactory behavior and their antennal extracellular response to odors will be studied in ORNs to examine the physiological site of the defect. Preliminary data indicate that mutant flies derived from an enhancer trap line with a P-transposon insertion near genes expressed in a subpopulation of antenna cells have an altered electrophysiological response to only one of seven odors tested. These studies will lay the groundwork for a molecular dissection of olfactory transduction and information processing in the antennal lobe and higher brain centers. The complete loss of the ability to smell (anosmia) or partial anosmia may be diagnostic for other deficits such as Alzheimer's disease and diminishes the quality of life. Concerning certain types of anosmia, the loss of specific mechanisms underlying olfactory transduction may be involved. In the future, gene therapy techniques which reintroduce normal genes into the accessible olfactory receptor cells may be used to correct specific defects; this therapy has been shown to improve lung function in cystic fibrosis patients.